Heterodimetallaboranes of Group 4 and 9 Metals: Analogues of Pentaborane(11) and Hexaborane(12)

Several early–late heterodimetallaborane clusters have been isolated and structurally characterized through spectroscopic and crystallographic analysis. The thermolysis of [Cp2Zr(BH4)2] (Cp = η5-C5H5) with [Cp*IrB3H9] (Cp* = η5-C5Me5) and [(Cp*Rh)2B2H6] yielded arachno-[(Cp2Zr)(Cp*Ir)B3H9] (2) and arachno-[(Cp2Zr)(Cp*Rh)B4H10] (4), respectively. In a similar fashion, the reaction of [Cp2Hf(BH4)2] was performed with the same set of group 9 metallaboranes that led to the formation of arachno-[(Cp2Hf)(Cp*M′)B4H10] (5: M′ = Ir; 6: M′ = Rh). To the best of our knowledge, 2 is the first structurally characterized pentaborane(11) analogue containing zirconium, while the clusters 5 and 6 are the first examples with Hf in a hexaborane(12) core. The bonding between the Zr atoms and the boron ring was studied computationally by DFT methods, and 2 can be defined as a dimetallic analogue of arachno-B5H11 on the basis of the combined experimental and computational results.